kusala9
commented
5 months ago Discussions with IEC at S-101PT, and othersl have reinforced the importance of taking into account any uncertianty in S-104 and S-102 (in the context of WLA and USSC) when depths are being substituted. These need to be included when the section taking quality into account (IMO requirement) is finally drafted in S-98 Annex C. This is related to, but not the same as, the original issue here but should be approached at the same time.
Handling of combined bathymetry quality parameters in ENDS (S-101, S-102 and S-104)
Text from email received during HSSC. This needs to be thought about and any enhancements added into S-98 Annex C. Have since confirmed with IEC that accounting for vertical uncertainty for WLA and USSC should be done, and grouped into the behaviours taking quality parameters into account (new IMO requirement).
Preconditions
Use case S-101 and S-102, example
7.2 m safety contour is generated using S-102. All grid cells equals and shallower than 7.2 m are surrounded by the safety contour. This will be the indicated safety contour.
The vertical uncertainty for the depth value 7.2 in the S-102 data set is calculated to ± 0.3 m. All grid cells shallower than 7.5 m but deeper than 7.2 m are shaded. The horizontal uncertainly is calculated to ± 5 m. All grid cells outside the other shaded grids cells are also shaded. All shaded grid cells (shaded by vertical and horizontal uncertainty) are surrounded by another contour. This will be the “worst case” safety contour.
The “worst case” safety contour must be used for alarms related to bathymetry in S-100 ECDIS in accordance with IMO Resolution MSC.530(106) ECDIS Performance Standards, Annex 1, 11.4.3. However, for alarms related to features in S-101 with the attribute horizontal clearance (e.g. bridges, overhead cables) the depth value 7.2 m must still be used.
The shaded area between the indicated safety contour and the “worst case” safety contour is the bathymetry uncertainty buffer zone and should be portrayed. Note: In some cases there will not be an indicated safety contour since the bathymetry uncertainty buffer zone can consist of grid cells deeper than 7.2 m, but equals or shallower than 7.5 m.
Use case S-101, S-102 and S-104 applying WLA
7.2 m safety contour is generated using S-102. In this case the water level is + 2 m, so All grid cells equals and shallower than 5.2 m are surrounded by the safety contour. This is the indicated safety contour.
The vertical uncertainty for the depth value 7.2 in the S-102 data set is calculated to ± 0.3 m and the vertical uncertainty for the water level is calculated to ± 0.6 m. All grid cells shallower than 6.1 m (5.2 + 0.3 + 0.6 = 6.1) but deeper than 5.2 m are shaded. The horizontal uncertainly in the S-102 data set is calculated to ± 5 m. Horizontal uncertainly of the S-104 data set is not applicable. All grid cells outside the other shaded grids cells are also shaded. All shaded grid cells (shaded by vertical and horizontal uncertainty) are surrounded by another contour. This will be the “worst case” safety contour.
The “worst case” safety contour must be used for alarms in S-100 ECDIS in accordance with IMO Resolution MSC.530(106) ECDIS Performance Standards, Annex 1, 11.4.3. However, for alarms related to features in S-101 with the attribute horizontal clearance (e.g. bridges, overhead cables) the depth value 5.2 m must still be used.
The shaded area between the indicated safety contour and the “worst case” safety contour is the bathymetry uncertainty buffer zone and should be portrayed.
Open questions (I am certain that there are many more…)